Furnace-lining.



G. S. DAVISON.

FURNACE LINING.

APPLgcATloN FILED 1uLY7.191s.

33921.@,415 Patented Jan. 2, 1917.

` miami.

Vun eras raar con.

S. DAYISON, QF PTTSURGH, PENNSYLVANIA, ASSIGNGR T ALLEN S. V'DAVIIISON COMPANY, 0F PITTSBURGH, PENNSYLVANIA, A CORPORATION 0F PENNSYLVANIA.

.appiieation med .iuiy 7, i916. serial no. ioaoaa 4 To all whom it may concern:

Be it known thatl', GEORGE Se. DavisoN, 'a citizen of the United States, residing at Pittsburgh, in lthe county of Allegheny and State of Pennsylvania, have invented cer-- tain new and useful improvements i'nflfurnace-Linings, of which the following is, a

specification.

'l his invention relates to furnace linings; rand it comprises as a new article of manufa'c'ture a granular mass of Vmatter composed off granules of substantial size of hard burnt a temperature of at least 3100 degrees F. or

higher, and during the period of exposure to the very high temperature is agitated in itli'e presence of an amount of basic slag or1 fot-her, v(relatively speaking) fusible, silicious iron-containing material which is merely that which can be taken up by the voids or g pores of such granules, the period of expoV sure of the granules and of the more fusible silicious material to such high temperature y being such as will insure the fused silicious material entering the pores of the granules by 'capillary attraction without lleaving a residue or coating of any substantial extent on the exterior of the granule; all as more fully hereinafter set forth and as claimed.

lin what is known as the basic open hearth method of refining iron and steel, the metal y is treated in a molten condition lin a reverberatory furnace by the conjoint inuence `fof lan oxidizing ame and of a basic material, lime. Y Under the influence of the flame theiron and its impurities undergo an oxidation and the acid constituents, phosphorus, sulfur, silicon, etc., are oxidized to the corresponding acid bodies which unite with the lime to form basic open hearth slag; a mterial which melts, ordinarily, at about 2900 degrees ll. although it sinters at lower lF'URNACE-LINING.

Patented Jan. 2, 119i 7.

I temperatures. The. temperature in the furnace is. in excess of this degree so that the slag is liquid. rlhe problem of lining furnaces of this character has been a serious one in the viron industry for many years. A suitable lining must, of course, be of basic material, toprevent attack by oxid of iron, the lime used in purifying, etc.; but on the other hand, while basic, it must not be subject to attack to any great extent by the acid bodies formed in the oxidation of the impurities of the iron, that is, silica, phosphoric acid, etc. Further, the lining must be of considerable mechanical strength in order to retain its place against the washing action of the iron, etc. The material must bond together in some way under the induence of the heat to give this mechanical strength; but it must not be otherwise substantially aiected, of course, by the heat.

The combination of characters is hard to obtain. rlhe best materials which have been hitherto found are'lcertain grades of rather impure magnesia from native magnesites. Pure magnesia is refractory; neither softening or melting at any temperature here involved; and it is a basic body, while at the same time it has no great tendency to lux.

and Waste away with the acid bodies produced in the oxidizing treatment of thel iron. But pure magnesia is so refractory that it cannot be used as a lining since its particles do not bond in the furnace. The particular varieties of magnesia which have been found suitable are those which contain a certain amount of silica and iron;-l

just enoughof thesebodies to produce under the heat of the furnace a slight degree of sintering throughout the granules and at their meeting faces. A lining of this inateiial in place consists in granules of magnesia in more or less open arrangement, united only at their meeting faces and with voids between them.v ln use, the voids on the surface -of the lining of course ll up with basic slag, but the voidsfarther removed from the surface do not, and remain open. The varieties of magnesite which are suitable to this purpose are notv common and are relatively costly. Very many efforts have been made to produce cheaper materials having approximately the same qualities; but most of the substitutes hitherto proposed have been open to one objection or l another.

considerable. i at the furnace'temperature the disadvan- One. substitute oft-enI proposed is the fluid basic slag. I have discovered that lated hard burnt ldolonfiitic lime or magne;

sian limeffa more or less variable` mixture" ofA lime and" magnesia which has been' exposed to, siich a high temperature as 4to shrink it and harden it. The shrunk dolo'- mitic limev has- Veven better mechanical, properties as regards strength "and" rigidity than the magnesite; but it is'g susc'eptibleH to the influence` ofthe atmosphere, taking up carbon-."dioxid an "moisture that is, 'it" tends to slake.`. 'It .n'ii1stl therefore beused at once after burn-ing. vndit does not bond well lining of hard 4burnt 'doloin the, furnace; a

ite! granules tamped intov place cannot be regarded Las permanent until-enoughbasic slagj` has flowed into the spaces between the granules to make'the whole'into a sort: of concrete in lwhich the binder or matrix is slag; and the aggregate, dolomite granules. And however well it may be tamped into place the proportion `of voids, and 'consequently of slag, in the finished lining is As' the 'slag is freely` fluid tage of'thfs .is obvious. In the effort to accelerate this lining-forming .operation it has :been proposed to make granular mixturesof dolomitic lime with enough granular `basic slagf to form the loinder or matrix without depending on the furnace, operationI Another proposition is to coat the dolomitegranules with .basic slag with the idea of l'making'asealin'g coating; -an impermeable coating which will shield the interior of' he granule and prevent lslaking actionszin storage or transportation. But neither of these propositions has beenl completelyf'successfuhand this is for the reason that the amount of slag necessary in both isl-too great. vIn use, either'the mixed granules orthe coated granules form 'a lining whichA is; like that 4previously described, .a e.. tweenlthe ,lime granules full of slag. Such a lining contains vtoo great a proportion of basicslag to make a highly desirable'lining in furnace. As` stated, basic slag vmelts M1290() degrees'F. andthe temperature of the furnace `is considerably in excess of this.

Therefore, with any such lining, the mixture tends to become moreor' lessY what may be described as mushy; the interior face l'of'the lining is really a freely fluid layer 'of molten slag, Vstiffene'd somewhat byv fthe presence of the infusible dolomite granules.

v takes place This is 'disadvantageous mechanically, and

there is the further .objection that the dolomite granules being, inefect, suspended in a :fluid bath of basic slag, -chemical action.

in short, a lining of the character described, 'is not as refractory as' it shouldbe. lAlthough it contains the fhighly refractory burnt dolomite granules, yet as a whole it is notmuch more refractory-than these'previo'us propositionsv for the use of basic slag and similar silicious bonding for dolomitic lime materials were wrong in ...principle, since the ,effort was in all cases `to have the bonding material present bel voids between" the several grains. It is not desirable in a good lining to have any such quantity of bonding agent present.- The granules should'be cemented at their mee ing faces by a 4hard and rigid union; but at the point any substantial amount'of the foreign bonding material; there should not be eno-ugh to form a highest temperature of the furnace. Insub-J sta-nce, granule should be unitedto .granule in the furnace sition of more fusible material, spacing them apart, and subject to displacement-by molten slag. In the present. invention,

. therefore, I restrict the amount of bonding agent to such an'amount as will merelysu-ffice at most to fill the pores and crevices of the granule and lproduce an' Yimpregnation of the granule as distinguished from any coating thereof; performing the impregnat- -ing operation at such va high'.temperature that theagent employed fis freelyifiud and maintaining' Sthis temperaturev suliiciently long to insure ,substantially the entire amount of such agent enteringthe pores by capillary or molecular attraction. Inso doing, i't is my object not vto leaveany sub- -stantialzfilm or coating layer of the agent on the 'exteriormf the granule, since, for reasons previously tate against-the quality of the lining pro- ;duce'd from ythe treated granules.; I have found-that with the pores impregnated as stated, the granules will bond at `meeting faces in the furnace without any necessity tween 'the faces of the granules; in suchl a manner and such quantity as to` fill the stated, this would miliofkunion there should not be liquid film of substantialthicliness between the meeting faces at eventhe lining without the interpofor 'the presence of any substantial layer p or ,film ofthe agent on suchfaces.

As the 'refractory granule, I 'may use dolomitic or magnesianv lime, lmagnesia, lime,- alumina, etc'. Even quicklime is suitvablefor the present -purposes'since the pores are 4filled and 4air cannot enter to slake vthe v material. I have found ,that an amount of. binderwhichis suf-` to fill the voidsof the i 's not enough tog-impair the rebasic7 slag and similari ficient substantially ranules y fractory qualities of dolomitic limetoV any 'material extent. v

i In a' specific .embodiment of the lpresen-t process, using dolomite or magnesian lime- Stone' and basic slag, dolomite is crushed to about the size.' of granule desired,'finer may terial b eing sifted out. With the granular materialthus'produced isv mixed about' 8 or f 9 per cent. of fine powdered ybasic open hearth slag or a correspondingv amount lof` other equivalent agents. Basic Islag con tams silicate of iron; and I nd that almost any material containing or capable of forming iron silicate will answer. As one of the equivalent agents I may' mention lsilicious iron ores, and particularlyI those of such composition as to resemble basic open hearth slag; mill cinder; etc. Any material containing both iron and silica and fusible at not too lo-w a temperature will answer; and-I contemplate the use of any such material. `The mixture of dolomite granules and powdered impregnated agent is fed into the upper end of a rotary kiln, or equivalent device and exposed 'to the action of a highly heated iame burning in aerial suspension vsomething like the flame in a cement kiln. But the temperatures here required are much higher than those used in cement kilns. A suitable flame of suitable temperature may be produced with powdered coal `burningwith su-perheated air; with naturalgas burning with a goodexcess of air, etc. Themixture of granules and powder passes downward through the kiln under the,heating influence of the flame and flame gases and a numberof reactions occur. -The dolomite is irst calcined, 'that is, freed of its carbon dioxid, and is then shrunk, that is, rendered dense, hard and strong. freely porous. When the temperature of the mixture under the influence of the radiant heat of the flame reaches 2900 degrees or higher, the slag melts lfreely and it is taken up or absorbed by the open pores of the lime, these pores being in large part formed by the expulsion of the carbon dioxid. I find that although the slag and Iriost other agents I use will melt at 280() or 2900 degrees F. it is advisable to use temperatures in excess of 3100` degrees in this incorporating operation so as to have a`s'utlciently thin liquidity of the slag to insure itsfreely entering the pores by capillarity without accumulating on the outside of the granules to fol'm any substantial skin Yor coat. At too low a temperature it is apt to collect more or less on the surface instead of enteringthe pores. As stated, I desire to have the slag inside the granule and not outside.

A` good article when cooled has a uniform f dark gray color while an excess of slag or a low-temperature operation gives granules of the black color of slag, the lighter colored lime not being visible through the coating.r

In this operation, the dolomite lis usually crushed to fragments of about th inch ,diameter fwhich contract to about gthsl; I have found that this `size of granule at a temperature of 3100o F. or about, with the circumstances obtaining inthe kiln operation, permits a tolerably uniform impregnation of the pores from side to side. With It vis howeverv taken up by the pores of the basic material while there must .still be enough to fill such pores with substantial completeness. The

binder should be very finely powdered inordervthat it may melt quickly and be uniformly distributed. Under. the described conditions of temperature and the like, any excess of binder, such an excess as would 'y produce any substantial coating on the outside, will be revealed-by more or less balling up of the material to form large aggregates. Where this happens,A the balled up material is discarded; but a careful control ofthe relative amounts of binder and basic granules will prevent any such action.

In stating that the granules of material are free from any substantial outside coating or-layer of binder, I wish it to be understood that I do not exclude the presence of some of the binder on the outside of the granule; enough, for instance, to produce a sort of very thin glaze; a glaze which is thin enough, inthe case of basic, slag, to allow the color of the dolomite to be lseen made under the present invention from a grayishwhite vdolomiticlime and a black slag, the color of the fragment is a dark gray; this color being substantially the same on the exteriorand on a freshly broken fractherethrough. In the besttype of material i ture. There is no visible appearance either of the light gray dolomite or ofthe black slag.

In the accompanying illustration I have shown more `or less diagrammatically 'one' type of apparatus which vmay be used 1n.. performing the present process.

The View is an elevation, partly in central vertical section, of an lorganization of apparatus elements embodying a' rotaryl kiln. In this showing, element 1 is a horizontal, rotary, slightly inclined cylinder entering at its upper end housing 2 provided with stack 3. Through this housing passes feed conduit. l entering the upper end ofv the kiln land supplied with material by conveyer 5 from' receptacle 6. At its lower end the kiln enters the usual type of movable housing 7. Through the front of this a housing enters burner 8 fed with gas, which may be natural gas, at l@ and air at 9. Treated granules drop through this housing into rotary cooler 1l.

In the use of the above described apparatus the kiln in its heated zones is maintained at a temperature of 310 or above, which may be effected by lsupplying natural gas at v with `plenty of air at 9. Grranulated dolomite and fine 'powdered basic slag in the requisite proportions are supplied to 6 and taken thence by 5 for delivery through 3 into the upper end of the kiln. The dolomite in' its passage down through the kiln is calcined, that is', deprived of its carbondioXid, which leaves it porous, and it is then, under high heat, shrunk materially and rendered hard, dense and firm but without losing its porosity. Thebasicv slag melts to a rial'to pass thin liquid which is taken. up bythe pores of the granules at or soon' after the time the porosity develops. `With the proper quan-v tity of ybasic` slagl and with the right tem-l perature the binder is all taken up in these pores, and the material passing from the hot zone will show substantially no local accumulationor skin 4or coating of slag;

,when cooled it will be of a uniform dark 4gray color without the black spots or surfaces which show the presence of what may be.. called free slag, that is, slag existing otherwise than' that absorbed in the pores of the material. The -hot impregnated slag drops at into cooler 11, which also serves as a preheater for air flowing up to the burning Zone. Since the material made under `this inventionA is very air heated by the material in the cooler materially aids in -producing the very high l kiln temperatures here necessary.

In a 12C-foot kiln having a diameter of 6 1, jfeet, `ordinarily it requires from about two and al half to Ythree hours for the mate- .from the feed end to the outlet end when the kiln is rotating at the rate of about 50 revolutions per hour.

' The .m'aterial'coming Afrom the 'rotary kiln may be cooled in any suitable manner. This is. advantageously done in "what is known as a clinker cooler in'the cement art. 'The unusually high'jtemperature' of the treatedV 1haterial and thehigh temperature required in vthe operation, lrender the regeneration of heat by .passing lair over the material and then into the kiln very advantageous.Y

The

cooled material 'may be bagged, stored, etc.,

withoutfear of deterioration or atmospheric influences. When used inthe open hearth furnace, under the heat of the furnace, the

'granules 'unite at their meeting faces to form anopen textured lining, much like 'that which is vformed by" the Lbest gradesbf magnesia frommagnesite, but even superior 'tol such amagnesia' lining, for the' reason that the union between the meeting faces, is,

lso tospeak, positive, instead of the more' or less 'accidental bonding occurring with these f impure magnesites.

' What I claim-is:--'7

" 1. As a furnace lining, a mass'of ygranular 'basic refractory material, the granules `bemg impregnated with a 'relatively small hot, return of` amount of silicious material but having their. faces free of any substantial layer" of such silicious material.

2. As a furnace lining a mass of granular basic refractory material, the granules being impregnated with a relatively small amount-y of material containing iron and silica but] havingtheir faces substantially free ofany substantial layer thereof. y v

3. As a furnace lining a mass of granular basic refractory material, the granules beingl Y impregnatedwith a relatively small amount of basic slag but having their faces substan- 'f tially free of any substantial layer thereof. 4. As a furnace lining a mass of granular basic refractory material, the granules having their-pores substantially filled with a relatively small amount of silicious material but having their faces relatively freeV of such silicious material,

5. As a furnace lining, a mass of granular basic refractory material," the granules hav- Ving their pores substantially filled ywith a relatively small amount of material containingironVA and silica but lhavingtheir faces substantially free thereof. `6. As a' furnace lining, a mass of gra-nular basic refractory material, the granules having their pores substantially lled with a relatively small amount of vbasic slag but having their faces substantially free thereof. 7 As a furnace lining, a mass of'granular hard burnt dolomitic lime, the granules being impregnated with. a relatively small amount of silicious material but. having their faces relatively free of such silicious material. 1

8. As a furnace lining a mass of granular hard burnt dolomitic lime, the granules be.- ingv impregnated with a. relatively small amount of material containing iron and silica but having their 4*faces substantially free thereof.

9. As a furnace lining avmass ofgranular hard burnt dolomitic'lime, the granules being impregnated with a relatively small amount of basic slag but having their faces substantially free thereof.

hard burnt vdolomtic lime, the granules havin their pores substantially filled -with a .re atively small amount ofv siliciousmaterial but having their faces relatively free of such silicious material.

1l. As a furnace lining, lar hard burnt dolomitic lime, the' granules having their pores substantially lled with a relativelysmall amount ofymaterial containing iro and silica but having their` faces substantially free thereof.

12. As a furnace dining, a mass of granuvlar hard burnt dolomitic lime, the granules having their poressubstantially -filled with a relatively small amount offbasic slag but vljuiving their ffaces substantially free thereof.`

a mass of-granu- '10. As a furnace'lining amass of granularl A small amount ofa powdered fusible material 4 containing a silicate of iron at a tempera! ture sufficient to render the latter material thinly fluid and maintaining the heat until such latter material is substantially entirely absorbed within the pores of the granules.

15. The process 'of making furnace lining material which comprises heating together a porous granular basic material with such an amount of a powdered fusible material as will sufce merely to lill the pores of such granular material without leaving an exterior excess, the heat being carried to suchy a temperature that such fusible silicious material will be rendered freely fluid enough to be taken up by the pores of such basic material with substantial completeness. l

16. rlhe process of making furnace lining material which comprises heating together a porous granular basic material with .such an amount of a powdered fusible silicious -material containing a silicate of iron as will suce merely to fill the pores of such granular material without leaving ani'exterior excess, the heat being carried to such a temperature that such fusible silicious material will be rendered freely fluid enough'to be taken up by the pores of such basic material with substantial completeness.

17. The rocess of making furnace lining material willich comprises heating together a porous granular hard burnt dolomitic lime with a small amount of a powdered fusibleV silicious material at a temperature sufficient to render the latter thinly fluid and maintaining the heat until such siliciousy material is substantially entirely absorbed within the pores of the granules.

18. rfhe process of making furnace lining f `material which comprises heating together a porous granular hard burnt dolomitic vlime with a small amount of a powdered fusible material'containing a silicate of iron at a temperature sufficient to render the latter material thinlyfluid andv maintaining the heat" until such silicate of iron is substantially entirely absorbed within the pores of the granules.

19. The process of making furnace lining material which comprises heating together a porous granular hard burnt dolomitic Vlime with vsuch an amount of a powdered Vfusible silicious material as will sufce merely to ll the pores of such granular material without leaving an exterior excess, the heat being carried to such a temperature that such fusible silicious material will be rendered freely Huid enough to be taken up by the pores of such hard burnt-lime with substantial completeness. y

20. The process of making furnace lining material which comprises heating together a porous granular hard burnt dolomitic lime with such an amount of a powdered fusible silicious material containing a silicate of'iron as will suliice merely to fill the pores of such granular material without leaving an exterior excess, the heat being carried to such a temperature that such fusible silicious material will be rendered freely fluid enough to .be taken up by' the pores of such hard burnt lime with substantial completeness. Y In testimony whereof, l ax my signature hereto, July 6, 1916. i

, en'onen s. Davison. 

